This invention relates to compositions for the coloring of fibrous articles, and more particularly to thickener concentrates for use in print pastes.
Pigment compositions for the printing of fibrous articles commonly contain thickening agents in order to assist in dispersion of the pigment, spreading of the composition over the substrate under operating shear conditions, and binding of the pigment to the fibrous article. It is common practice in the formulation of such pastes to first prepare a concentrate of the thickener, known in the art as a "clear concentrate". Generally, a clear concentrate is an aqueous mixture, such as a dispersion or solution, containing a high concentration of the thickener, on the order of about 20-50% by weight. Because conventional thickeners at such high concentration form highly viscous mixtures which cannot be easily handled, the next step is to dilute the clear concentrate to form a "cut clear". This is a composition containing about 5% by weight of the clear concentrate, the balance being water. In the next step of formulating the paste, a pigment concentrate (known in the art as a "presscake dispersion") is mixed with the cut clear and water in such proportions as to provide a viscosity of about 1,000-8,000 cps. A common presscake dispersion contains about 35% by weight of pigment, about 12% by weight of dispersants for the pigment, and the balance water. The resulting composition is known as a "color concentrate" and conventionally contains about 50% by weight of the presscake dispersion, about 10% by weight of the clear concentrate and the balance water. For use as a pigment printing paste, a resinous binder is then mixed with the color concentrate and the mixture is diluted to a level effective to obtain a viscosity increase suitable for providing good printability.
In the case of print pastes other than pigment print pastes, the color concentrate is formed with a suitable water soluble dye rather than with a presscake dispersion, and the print paste is prepared merely by diluting the color concentrate. A resinous binder is not required.
It will be evident from the foregoing that the thickener must be carefully selected from the standpoint of its viscosity in water. It must be present in the color concentrate at levels effective for assisting in the dispersion of the dye but without inducing so high a viscosity that the composition becomes unmanageable in terms of mixability and rheological properties. Accordingly, an essential requirement for any thickener is that it have a controllable viscosity, i.e., the viscosity which it imparts to a formulation may be increased or decreased predictably upon the addition or subtraction of water.
A wide variety of thickeners are known. These include natural gums such as guar and locust bean extract, certain polyelectrolyte resins, carboxyvinyl polymers, and copolymers containing hydrophobic groups based upon stearic acid and hydrophilic linkages based upon poly(oxyethylene) chains. All of the known thickeners have deficiencies. These include undue sensitivity of the ionic thickener types to pH and salts, poor thickening efficiency, handling and formulating difficulty due to too high initial viscosity or too long a duration for full viscosity development, the tendency of some thickeners to stiffen fabrics or to cause "haloing" (diffusion of color patterns) or "crocking" (rubbing off of color), and other aspects of poor viscosity control such as lack of viscosity recovery after the high shear which accompanies the screening of a pigment printing paste. Even those thickeners which are non-ionic, and therefore not normally subject to changes in pH or the presence of electrolytes, have been deficient in storage stability, exhibiting substantial losses in viscosity due to hydrolysis on standing.